Compiler: The multi assign treeopt fix was broken.

The fix for #10006 (closed) causes warnings in Nettle:

Pike v8.1 release 13 running Hilfe v3.5 (Incremental Pike Frontend)
> Nettle.Hash;
/home/grubba/src/Pike/8.1/lib/modules/__builtin.pmod/Nettle.pmod/Hash.pike:1280: Warning: An expression of type array(int | string) cannot be assigned to a variable of type array(int | string(8bit)).
/home/grubba/src/Pike/8.1/lib/modules/__builtin.pmod/Nettle.pmod/Hash.pike:1281: Warning: Expected: array(int | string(8bit)).
/home/grubba/src/Pike/8.1/lib/modules/__builtin.pmod/Nettle.pmod/Hash.pike:1281: Warning: Got     : array(int | string).

The code that is warned about:

    if (!catch([r, salt, iters] = [array(string(8bit)|int)]
                                   array_sscanf(line, format))